No abstract

Carbon fixation under wetland anaerobic soil conditions provides unique conditions for long‐term storage of carbon into histosols. However, this carbon sequestration process is intimately linked to methane emission from wetlands. The potential contribution of this emitted methane to the greenhouse effect can be mitigated by the removal of atmospheric CO2 and storage into peat. The balance of CH4 and CO2 exchange can provide an index of a wetland's greenhouse gas (carbon) contribution to the atmosphere. Here, we relate the atmospheric global warming potential of methane (GWPM) with annual methane emission/carbon dioxide exchange ratio of wetlands ranging from the boreal zone to the near‐subtropics. This relationship permits one to determine the greenhouse carbon balance of wetlands by their contribution to or attenuation of the greenhouse effect via CH4 emission or CO2 sink, respectively. We report annual measurements of the relationship between methane emission and net carbon fixation in three wetland ecosystems. The ratio of methane released to annual net carbon fixed varies from 0.05 to 0.20 on a molar basis. Although these wetlands function as a sink for CO2, the 21.8‐fold greater infrared absorptivity of CH4 relative to CO2(GWPM) over a relatively short time horizon (20 years) would indicate that the release of methane still contributes to the overall greenhouse effect. As GWPM decreases over longer time horizons (100 years), our analyses suggest that the subtropical and temperate wetlands attenuate global warming, and northern wetlands may be perched on the “greenhouse compensation” point. Considering a 500‐year time horizon, these wetlands can be regarded as sinks for greenhouse gas warming potential, and thus attenuate the greenhouse warming of the atmosphere.

The importance of vegetation in affecting CH4 emissions was investigated in a Carex‐dominated fen located near Schefferville, Quebec, and in the Experimental Lakes Area, Ontario. Comparison of emission rates with and without the presence of aboveground vegetation indicated that over 90% of the emission was plant‐associated transport. Further evidence of this association was found in a linear correlation of CH4 emission with aboveground plant biomass (R=0.93). To test the importance of aboveground plant photosynthetic production on methane production, aboveground vegetation was clipped from sites continually over the growing season. Both emissions and dissolved pore water CH4 were reduced relative to adjacent vegetated areas. A significant correlation (R=0.93) of CH4 emissions with net CO2 exchange in this fen gives evidence of the close association between new plant production and methanogenesis.

Abstract. We analyzed the relationship between net ecosystem exchange of carbon dioxide (NEE) and irradiance (as photosynthetic photon flux density or PPFD), using published and unpublished data that have been collected during midgrowing season for carbon balance studies at seven peatlands in North America and Europe. NEE measurements included both eddy-correlation tower and clear, static chamber methods, which gave very similar results. Data were analyzed by site, as aggregated data sets by peatland type (bog, poor fen, rich fen, and all fens) and as a single aggregated data set for all peatlands. In all cases, a fit with a rectangular hyperbola